Poly(butylene terephthalate) (PBT) is a strong semicrystalline thermoplastic. It has excellent thermal and chemical resistance, good dimensional stability, low moisture absorption, and good electrical and mechanical properties. Because of its good processibility, PBT is widely used in a variety of applications, most commonly in durable products that are formed by injection molding or extrusion, such as electronic equipment, automotive parts, medical devices, and textiles (Gallucci et al., Poly(butylene terephthalate), Modern polyesters: Chemistry and Technology of Polyesters and Copolyesters, 293-322, Wiley: West Sussex, 2003).
As a cost-effective engineering material, nonwoven fibers of PBT have been used for filtration medium (Hutten, Processes for Nonwoven Filter Media, Handbook of Nonwoven Filter Media, 195-244, Elsevier: Burlington, Mass., 2007), composite materials (Zuo et al., ACS Macro Lett. 2013, 301-305; Doan, V. A.; Nobukawa et al., Composites Part B 2012, 43(3), 1218-1223; Saligheh et al., J. Macromol. Sci., Phys. 2011, 50(6), 1031-1041; Guo et al., J. Appl. Polym. Sci. 2013, 12 (6), 3652-3659; Kim et al., J. Biomed. Mater. Res. Part B Appl. Biomater 2009, 849-856; Risbud et al., Biomaterials 2001, 22(12), 1591-1597), and tissue scaffolds (Catalani et al., Macromolecules 2007, 40(5), 1693-1697; Woodfield et al., Biomaterials 2004, 25(18), 4149-4161; Ikada et al., Macromol. Rapid Commun. 2000, 21(3), 117-132; Hollister et al., Nat. Mater. 2005, 4(7), 518-524). They can be fabricated by melt blowing (Ellison et al., Polymer 2007, 48(11), 3306-3316), electrospinning (Saligheh et al., J. Macromol. Sci., Phys. 2011, 50(6), 1031-1041), melt spinning (Chen et al., J. Appl. Polym. Sci. 1987, 33(4), 1427-1444), and forcespinning (Shanmuganathan et al., ACS Macro Lett. 2012, 1(8), 960-964).
Among these techniques, melt blowing is of particular interest, because it does not require solvent. It is widely used and applicable to many polymers. A typical melt blowing process starts with extrusion of a molten polymer through a die. Jets of hot air entrain the molten polymer filament and rapidly extend its length with concomitant reduction in diameter. A significant amount of ambient air, which is entrained by the hot jets, leads to rapid cooling of the fiber below its solidification temperature (i.e. glass transition temperature or crystallization temperature). Thus fibers are formed between the extrusion temperature and solidification temperature, and finally fiber mats are collected on a static or continuous screen.
Although PBT nonwoven fibers have found uses in a variety of fields, its surface properties, such as wetting, biocompatibility, and adsorption, may not meet the requirements for various applications. Therefore, surface modification plays an important role in improving the surface properties and enhancing the performance of PBT nonwoven fibers. Several techniques have been applied to impart either enhanced hydrophilicity or superhydrophobicity to PBT or other polymeric fibers, such as coating with hydrophilic/hydrophobic chemicals or particles (U.S. Pat. No. 7,524,425; Ramaratnam et al., Chem. Commun. 2007, (43), 4510-4512; U.S. Pat. No. 7,842,624; Shin et al., Soft Matter 2012, 8(6), 1817-1823), physical vapor deposition (PVD) (Jiang et al., Surf. Coat. Technol. 2010, 204(21-22), 3662-3667; Huang et al., J Mater Sci 2007, 42(19), 8025-8028), chemical vapor deposition (CVD) (Ma et al., Macromolecules 2005, 38(23), 9742-9748), blending in low-surface-energy additive (Hardman et al., Macromolecules 2011, 6461-6470), copolymerization (U.S. Pat. No. 7,736,516; Ma et al., Langmuir 2005, 21(12), 5549-5554), surface grafting (Fareghi et al., Iran. Polym. J. 2013, 22(5), 361-367; Bongiovanni et al., Colloids Surf, A 2013, 418(0), 52-59), layer-by-layer (LBL) deposition (Li et al., Cellulose 2012, 19(2), 533-546), sol-gel technique (Vasiljević et al., Cellulose 2013, 20(1), 277-289; Raghavanpillai et al., J. Fluorine Chem. 2012, 135(0), 187-194), and plasma treatment (Fernández-Blázquez et al., Adv. Colloid Interface Sci. 2011, 357(1), 234-238; Wei et al., J. Membr. Sci. 2012, 407-408(0), 164-175; Salvagnini et al., J. Biomater. Sci., Polym. Ed. 2007, 18(12), 1491-1516; Gérard et al., J. Polym. Sci., Part A: Polym. Chem. 2011, 49(23), 5087-5099; Liu et al., J. Membr. Sci. 2013, 428(0), 562-575).
The modifications of fiber mats are described in U.S. Pat. Nos. 3,017,685; 3,096,557; 3,111,359; 3,135,577; 3,287,787; 4,008,044; 4,803,256; 4,842,792 and 5,124,205. In addition, alkaline hydrolysis has been studied on poly(ethylene terephthalate) (PET) fabrics to modify their surface wetting property (Ng et al., Process Biochem. 2009, 44(9), 992-998; Hadjizadeh et al., J. Mech. Behav. Biomed. Mater. 2010, 3(8), 574-583; Shukla et al., J. Appl. Polym. Sci. 2000, 75(9), 1097-1102; Dave et al., J. Appl. Polym. Sci. 1987, 33(2), 455-477; Holmes et al., J. Appl. Polym. Sci. 1995, 55(11), 1573-1581; Kotek et al., J. Appl. Polym. Sci. 2004, 92(3), 1724-1730; Tavanai et al., J. Text. Inst. 2009, 100(7), 633-639; Kim et al., J. Appl. Polym. Sci. 2009, 112(5), 3071-3078). However, it was unknown whether alkaline hydrolysis is applicable to the modification of PBT nonwoven fibers, as PBT woven fabrics are more resistant to sodium hydroxide solutions than PET woven fabrics (Shukla et al., J. Appl. Polym. Sci. 2000, 75(9), 1097-1102).